A yucca plant can be difficult to remove completely from your yard. They have complex root systems and if you are unable to get out all of the roots, the plant will grow back. If you dig too much and make a lot of root cuts you are actually causing propagation of the plant and will have a lot of new growth the next growing season. There are steps that you can follow to help ensure that you get all of the roots out.
Step 1 - Prune
Remove the top growth and greenery of the yucca plant. Take the pruners and cut all of the plants that you are removing to the top of the root. This will make things easier on you and keep from getting eaten up by the rough and sharp edges of the plant.
Step 2 - Water
It is easier to remove roots from the ground when the soils and plant are well watered. The roots will slide out of the soil easier and will have less breakage, giving less chance for re-growth.
Step 3 - Dig
Dig a very wide hole around the yucca plant, at least two if not three times wider than the plant itself. Dig carefully and try not to cut through any roots. Use the shovel and the pick to loosen the surrounding soil. Carefully loosen and dig and you will be able to get most of the root out when you initially lift the plant out of the ground.
Step 4 - Search
Once you have lifted the main root system from the ground you will need to search for sections of root that have branched off and started forming new extended root systems. Be meticulous in getting rid of the roots. Pull out roots, even if they seem too small to grow back.
Step 5 - Apply Stump Killer
The yucca root is very strong. If you want to make sure that it does not come back next year, then you will need to kill any roots left in the soil. By using a stump killer instead of a standard plant and weed killer you can help to guarantee no re-growth. There will, of course, be no growth of other plants in this area as well. The time that you need to wait to re-plant is shorter than waiting until next growing season to realize that you still have yucca growing in the exact same spot.
Some people have a hard time getting rid of all of the roots. It is a difficult process and if you are not completely thorough, the plants will come back stronger than ever. You can deprive the plant of sun and water until they succumb on their own or completely cover the root system with plastic and build a raised flowerbed over the top of where the plant was. You can also go as far as removing the whole section of plantings and replace it with fresh topsoil. The whole process can take many hours over several days depending on how integrated your plants are into the landscape.